The subject matter disclosed herein relates generally to motor heaters, and, more particularly, to a motor controller having a power structure controllable to heat motor windings.
The use of induction motors for driving equipment, such as oil pumps, irrigation pumps, and the like, has presented certain problems when used in areas where humidity is present. Generally these motors may be operated for long periods of time and become hot, and then are turned off for given periods according to the particular application. When these industrial-type motors are turned off, moisture from the surrounding atmosphere tends to condense within the motor as the motor cools. This moisture can be very harmful to the motor windings and many efforts have been made to help eliminate the moisture condensation. For example, space heaters and other types of radiant heaters have been employed to maintain the temperature of the motor an order of 5 degrees to 20 degrees Celsius above the normal ambient temperature so that condensation will not form after the motor has been turned off. However, interior portions of the motor are not always maintained at such an elevated temperature so that condensation nevertheless can form on internal motor parts.
An improved concept has been the use of a dedicated motor winding heater device to apply a small current, considerably less than the rated amperage of the motor, fed into the electrical input leads of the motor after the motor has been turned off. This small current is intended to keep the interior of the motor at an elevated temperature and thus reduce the problem of condensation. However, such dedicated devices can be somewhat complicated, and add cost and size to the system. First, the dedicated motor winding heater device must be connected across the input electrical leads of the motor and it is possible that the heating unit itself may be damaged if the normal input power to the motor should be applied to these leads inadvertently. In addition, it is necessary that the motor be switched off before the application of any heating current to the interior of the motor from the unit as otherwise there can be generated a back voltage when the motor is still in motion which could damage the unit.
There is a need, therefore, for an improved technique for heating motor windings. There is a particular need for a motor winding heater configuration that does not require the use of additional independent motor winding heater devices.